Multirange radio receiver



April 6, 1937. w. VAN B. ROBERTS MULTIRANGE RADIO RECEIVER 2 Sheets-Sheet 1 Filed Nov. 15, 1932 5 N E Y R .h. W E 05 1 N mm E V H Vvn A N E U A W Y B MEL A'pril 6, 1937. w. VAN B. ROBERTS MULTIRANGE RADIO RECEIVER Filed NOV. 15, 1952 2 Sheets-Sheet 2 INVENTOR WALTER VAN B. OBERTS BY Mi ATTORNEY Patented Apr. 6, 1937 MULTIRANGE RADIO RECEIVER Walter van B. Roberts, Princeton, N. 3., assignor to Radio Corporation of America, a corporation of Delaware Application November 15, 1932, Serial No. 642,693

6 Claims.

This invention relates to an improved method of switching from a signalling system, or circuit, arrangement adapted to be tuned over one range offrequencies to a system adapted to be tuned over a different range.

In the prior art it has been common practice to use one and the same tuning condenser for several ranges of frequencies, the switching from one range to another being accomplished by 10 changing coils either by manual removal and replacement (the so-called plug-in coil method), or by electrically switching in other coils. The undesirable features of this practice, and which this invention has as one of its objects to avoid,

5 are several.

In the first place, it is undesirable to use the same tuning condenser in a plurality of frequency ranges, because, if its reactance is suitable at the lower frequency ranges, it will be too small for efficient operation at very much higher frequencies. Again, a given condenser will vary the tuning of a circuit over approximately as great a percentage variation of frequency in the high frequency ranges as in low frequency ranges;

this results in a very much greater crowding together on the tuning dial of the various stations in the higher frequency ranges than the lower ones, since stations are separated more nearly on a basis of uniform actual frequency separation than uniform percentage frequency separation.

In the second place, the lack of a good permanent joint between coil and condenser in an oscillatory circuit makes likely noises due to imperfect electrical connection in the low resistance oscillatory circuit. In the third place, changing coils by the plug-in method is slow and tedious, while electrical switching as employed heretofore necessitates the existence of considerably more wiring than readily tolerable in receivers for very high frequency ranges. This wiring not only makes it more difiicult to tune the circuits to very high frequencies, but also increases the coupling effects between coils in use and those not in use, and, thus, leads to an undesirable absorption of energy from the active coils by those not in use.

To avoid the above mentioned drawbacks, I prefer to use a separate complete oscillatory circuit for each frequency range, the variable element thereof being designed to tune the circuit between the exact limits desired for the particular range in question. The magnitude of the oscillatory circuit elements are chosen to give not only the desired tuning range, but also the stiffness, or ratio of inductance to capacity, best suited for efficient operation in the said range in question.

In addition to the drawbacks heretofore discussed, further difficulty sometimes arises from 5 the attempted use of one and the same circuit element over a wide range of frequencies. For example, a by-pass condenser which has a low impedance at broadcast frequencies may develop a high impedance at very high frequencies due to 10 internal resonance efiects, while a condenser; of small enough dimensions and capacity for satisfactory operation at high frequencies may be of too low a capacity for satisfactory by-passing of lower frequencies. The same type of difiiculty 15 may arise in connection with choke coils, or even resistances. In accordance with the present invention, these further diificulties are avoided by providing wherever necessary separate circuit elements for each frequency range.

Hence, one of the main objects of the present invention is to minimize undesirable stray capacities and coupling effects in a radio receiver designed to allow convenient switching from one frequency range toanother.

A further important object is to provide means in a radio receiver for switching into operation different elements of the same type for different frequency ranges wherever a single element of the type is not adapted to operate most efiiciently 30 in more than one range.

Another object is to provide a plurality of controls for the various ranges of a receiver so that manipulation of the controls when operating in one range will not affect the adjustment of the 6 controls used for tuning over another range, this permitting the operator to switch instantly from a station in one range to a station in another range without any adjustment of tuning, orother controlelements, provided the aforesaid stations 40 have each been previously tuned in.

Still another object is to provide a switching arrangement of the kind described wherein the oscillatory circuits carrying the relatively large radio frequency currents need not be broken by switch contacts, and thus to avoid the introduction of deleterious and variable values of contact resistance at points where resistance is particularly undesirable.

Further objects are to provide a simple and 50 readily operable band switching arrangement for a radio receiver, and to arrange positive and unmistakable means for indicating at all times in which range the receiver is operating.

Briefly, the means provided in accordance with 55 the present invention for avoiding all the various difiiculties discussed heretofore consists in a switching arrangement for a multi-range radio receiver which permits the circuit elements individual to the various ranges to be well shielded and spaced from each other to avoid static or magnetic couplings therebetween, while not requiring long connecting wires which would reintroduce by their proximity to each other the very coupling effects which shielding and spacing are utilized to avoid.

The novel features which I believe to be characteristic of my invention are set forth in particularity in the appending claims, the invention itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken in connection with the drawings, in which I have indicated diagrammatically several circuit organizations whereby my invention may be carrie into effect. 7

In the drawings Figure 1 illustrates in diagrammatic form an embodiment of a multi-range receiver which in- 2 corporates certain features of the present invention; Figure 2 is a diagrammatic representation of another embodiment of the invention; Figure 3 shows a control panel of a receiver including the invention; and, Figure 4 combines the systems shown in Figures 2 and 3, and in addition, illustrates an additional range.

Referring to the drawings, there is shown in Fig. 1 a schematic diagram of a simple form of radio receiver employing one stage of tuned radio frequency amplification, a regenerative detector, and one stage of audio amplification followed by a reproducer. It will be seen that two sets of tuned circuits with their appropriate primary coils and tickler coils, two volume control potentiometers, two regeneration controls 9 and I0, and two grid leak condenser combinations for grid side detection are shown. Switches are also shown for switching the grid and plate elements of the tubes and antenna into contact with the 5 appropriate elements.

Assuming that the switches are in the position shown, it will be seen that through switch I the antenna A is connected to coil L which is coupled to tuned circuit I including variable tuning 5 condenser C1. The ungrounded side of tuned circuit I is connected through switch 3' to the grid of the amplifier tube I6. The screen electrode I6 of the amplifier tube I6 is connected to the volume control potentiometer II through switch I'I, while the plate is connected through switch I8 to the primary 5 which is coupled to the tuned circuit 2.

The latter includes the tuning condenser C2 and is connected through its individual grid leak condenser combination C3 to the control grid of the detector tube I9. The switch 20 is used for connecting the tuned circuit 2 to the grid of tube I9.

The plate of the detector tube I9 is connected by switch 2| to feed-back coil I, it being understood that coil is magnetically coupled to tuned circuit 2. The feed back coil 1 is shunted by the regeneration control variable resistor 9. The detector plate circuit is then completed through a radio frequency choke L2, and the primary L:

of the audio frequency transformer M1, radio frequency current being shunted to ground through the radio frequency by-pass condenser l3.

If now all the switches I, 3, I8, I1, 20, 2| are thrown to the other position shown, the receiver circuit arrangement will be exactly the same as before, but a new set of tuned circuits 3, 4 will be thrown into operation, these latter circuits being designed for most eflicient operation in a different frequency range. The new volume and regeneration control elements I2, III will also be switched into operation so that if the switches are thrown back to the original position the volume regeneration and tuning controls for the first described frequency range will not have been altered by switching over to and operating in the second frequency range. While the diagram shows only two frequency ranges, it is obvious that any number may be used. The dotted lines 22 connecting the rotors of condensers C1 and C2 provide uni-control in one range; the uni-control 23 provides uni-control tuning in the other range.

Fig. 1 does not however illustrate an embodiment of the invention, as it will be evident that if a large number of tuning ranges is employed there will be required a considerable length of wire running from the switches to the circuit elements, and this wire together with the capacity between adjacent switch points constitutes a sufiicient coupling between the circuits of the various frequency ranges to make possible the absorption of energy of certain frequencies from the circuits in operation by one or more of those not connected in operation. The multi-receiver arrangement of Fig. 1 is shown to illustrate the manner of embodying the present invention in a receiver.

Fig. 2 shows the means employed to avoid the aforesaid undesired coupling effects, and to permit switching while maintaining extremely short paths for the radio frequency connections external to the tubes. The numeral I4 designates a switch arm rotatable by a hollow shaft I5 which is perpendicular to the plane of the drawings. Tube I6, which is the radio frequency amplifier tube of Fig. 1, is mounted on rotatable arm I4, and its cathode is heated by flexible heater wires 30 passing through the hollow shaft I5 to the heating source (not shown). The antenna leadin wire 3I from the antenna A (not shown in Fig. 2) is also brought through the hollow shaft I5, and connected to switch point I which is rigidly attached to switch arm I4. The other elements of the tube are similarly connected to switch points 3, I8, I! which engage with contacts connected to the various external circuit elements shown in Fig. 1.

The numeral I8 designates a similar rotatable switch arm carrying detector tube I9. The arms I8 and I I are preferably mounted in parallel planes, and are uni-controlledly actuated by the same shaft I5. That is, the hollow shaft I5 has mounted on it, in spaced parallel relation, the arms, or planes, I l and I8 supporting the tubes. In the drawings only one frequency range is shown. It should be clearly understood that as switch arms I4 and I8 are rotated, the switch points carried by them move around and engage an entire new set of contacts to the circuits of a different frequency range. Thus, the other group of contacts of Fig. 1 would be engaged. It will be seen that regardless of which set of circuits the tube is connected to, the leads from the elements of the tube to the circuit elementsare maintained extremely short while the groups of circuit elements for the various frequency ranges may be kept as far apart as desired by locating them around the circumference of a sufiiciently large circle. In addition to keeping these groups of elements well separated it is desirable to employ metallic shielding between groups.

Fig. 3 shows a preferred form of the arrangement of the front of the operating panel for a receiver having four frequency ranges. Knob 40 which rotates the switch arms M and I8 by means of shaft is provided with a pointer 4! which indicates the frequency range connected in circuit. Each frequency range is provided with three controls, via: a tuning condenser of the gang type which tunes all the circuits of the range (K1K2K3K4), a volume control H, and a regeneration control 9'. In the condition illustrated in Fig. 3 the range selector knob 48 is adjusted to bring the frequency range 550 to 1500 kilocycles into operation.

In order to shift from this range to a short wave range, for example 3 to 6 megacycles, it is only necessary to rotate knob All until the pointer is aimed at the lower set of controls. If one station is tuned in on the higher frequency range, and another is tuned in on the lower frequency range it is possible to switch back and forth from the one station to the other by merely turning knob back and forth, and without any further adjustments of the tuning, volume, or regeneration controls of either range.

In Figure 4 there is shown a diagrammatic sketch illustrating how the systems shown in Figures 2 and 3 may be combined in a radio receiver. It will be noted that Figure 4 shows an additional range, and that provision is made on the panel to connect two, more ranges. These have not been shown since to do so would unnecessarily complicate the drawings. The principles of the invention, however, are believed to be clearly discussed in Figure 4.

In view of the detailed description of the systems shown in Figures 2 and 3, matter shown in Figure 4 is believed to be self-explanatory.

While I have indicated and described several systems for carrying my invention into effect, it will be apparent to one skilled in theart that my invention is by no means limited to the particular organizations shown and described, but that many modifications may be made without departing from the scope of my invention as set forth in the appended claims.

What I claim is:

1. In a multi-range radio receiver a panel. at least one high frequency amplifer tube and a detector tube mounted behind the panel, the amplifier tube being provided with at least two independent tunable input circuits and two independent output circuits, said detector being provided with at least two independent tunable input circuits and at least two independent output circuits,

means for tuning one of the amplifier and detector input circuits through a common frequency range, additional means for tuning the remaining input circuits of said amplifier and detector through another frequency range, means including an operating lever mounted so as to project through the panel for selectively connecting the 7 amplifier tube and detector tube to either of said circuits of the same range, said means comprising a device for displacing said amplifier tube and detector tube with respect to said circuits.

2. In combination, a pair of resonant oscillatory circuits, means for tuning said circuits through a common frequency range, an electron discharge tube provided with means for coupling said circuits, an additional pair of oscillatory circuits, means for tuning the latter circuits through a different frequency range, and means including a support for said tube which is movable with respect to said circuits for connecting the electrodes of said tube at will to either of said pairs of circuits, a pair of independent control devices for varying the potential of at least one of the electrodes of said tube, and means carried by said movable support for connecting said tube electrodes to either of said control devices.-

3. In combination, in aradio receiver, a multielectrode amplifier tube, a pair of independent signal input circuits each tunable through a different frequency range, a switch provided with a movable element for connecting an input electrode of said tube to either of said input circuits, a pair of independent load output circuits, each of said output circuits corresponding to one of said input circuits, a switch provided with a movable element for connecting an output electrode of said tube to the output circuit corresponding to the input circuit connected to the tube input electrode, means for connecting the movable elements of said switches to said tube, and means for moving the tube to actuate said switches.

4. In a multi-range radio receiver, of a type comprising a plurality of independently tunable networks, each network comprising a series of cascaded resonant circuits tunable through a common frequency range, and said networks being tunable through different frequency ranges,

independent volume control and regeneration control devices connected with each network, a plurality of tubes common to all of said networks, and a common means for simultaneously and selectively moving said tubes into electrical connection with any of said networks whereby the receiver may be switched from a station in one range to a station in another range without tuning, volume, or regeneration adjustment.

5. In a multi-stage radio receiver, of a type comprising a plurality of independently tunable networks, each network comprising a series of cascaded resonant circuits tunable through a common frequency range, and said networks being tunable through different frequency ranges, independent volume control and regeneration control devices connected with each network, a plurality of tubes common to all of said networks, and a common means for simultaneously and selectively moving said tubes into electrical connection with any of said networks whereby the receiver may be switched from a station in one range to a station in another range without tuning, volume, or regeneration adjustment, and a visual device associated with at least one of said tubes for indicating which of said networks is in operation.

6. In a radio receiver for operation in a plurality of frequency bands, a thermionic discharge tube and a group of tunable circuits adapted in cooperation with said tube to tune said receiver over a first range-of frequencies, each of said circuits comprising a coil and a variable tuning condenser permanently connected together, a second group of tunable circuits each comprising a coil and variable tuning condenser permanently connected together and adapted in cooperation with said tube to tune said receiver over a second range of frequencies, individual terminals for a tuned circuit of each group cooperating terminals for said thermionic discharge tube, and means including said individual terminals and the cooperating thermionic discharge tube terminal for selectively operatively connecting said tube with either of said groups of tuned circuits characterized by relative motion between said tube and said circuits, said last means being constructed and arranged to cause sumcient physical displacement so that the terminals of the tuned circuits of the group not associated with said tube are relatively widely spaced from the terminals of said tube while the terminals of the group of circuits associated with said tube are relatively closely adjacent to the terminals of said tube to thereby prevent appreciable electric coupling between the said groups and between component parts of a tuned circuit in one group and the component parts of a tuned circuit of the other group, and also between a terminal of a circuit of one group, and a terminal of a circuit of the other group.

WALTER VAN B. ROBERTS. 

